问题
I want to take a piece of code, copy it into a global array and execute it from there.
In other words, I am trying to to copy a bunch of instructions from the code-section into the data-section, and then set the program-counter to continue the execution of the program from the data-section.
Here is my code:
#include <stdio.h>
#include <string.h>
typedef void(*func)();
static void code_section_func()
{
printf("hello");
}
#define CODE_SIZE 73
// I verified this size in the disassembly of 'code_section_func'
static long long data[(CODE_SIZE-1)/sizeof(long long)+1];
// I am using 'long long' in order to obtain the maximum alignment
int main()
{
func data_section_func = (func)data;
memcpy((void*)data_section_func,(void*)code_section_func,CODE_SIZE);
data_section_func();
return 0;
}
I might have been naive thinking it could work, so I'd be happy to get an explanation why it didn't.
For example, after a program is loaded into memory, does the MMU restrict instruction-fetching to a specific area within the memory address space of the process (i.e., the code-section of the program)?
For the protocol, I have tested this with VS2013 compiler over a 64-bit OS and an x64-based processor.
Thanks
回答1:
Windows (and many other modern OSes) by default sets the data section as read/write/no-execute, so attempting to "call" a data object will fail.
Instead, you should VirtualAlloc a chunk of memory with the PAGE_EXECUTE_READWRITE
protection. Note, it may be necessary to use FlushInstructionCache to ensure the newly-copied code is executed.
来源:https://stackoverflow.com/questions/25311861/execute-a-piece-of-code-from-the-data-section